A method of preparing TEM lamellae is known from international application WO2008/051937 A2. A device for preparing TEM lamellae is disclosed in international application WO2008/051880 A2, the contents of which is hereby incorporated by reference in its entirety. Patent application US 2008/0054179 A1 discloses a method of lamellae preparation employing chemical vapor deposition. Patent application US 2004/0016880 A1 discloses an earlier method of lamellae preparation.
It has been found that in the application of a focused ion beam, scattered, back-scattered and secondary ions present a problem insofar as they lead to amorphisation and gradual erosion of the original sample in particular at the upper edge of the lamella. Furthermore, a contamination with the ions of the beam, e.g. Ga ions, may occur. To prevent his, a local protection strip may be applied to the upper narrow edge of the lamella before beginning with the ion milling to both sides of the protection strip.
To this end, initially a platinum or tungsten strip may be generated via electron beam induced gas phase deposition EBID. The actual protection strip may then be applied onto this strip using ion beam induced gas phase deposition FIB. Depositing the protection strip via FIB without preceding electron beam deposition would lead to the previously mentioned effects, erosion and amorphisation. Following FIB deposition, the substrate is milled on both sides towards the protection strip, leaving only the lamella with the thin protection strip on top. The lamella can then be fastened to a tungsten tip of a nano manipulator via ion beam assisted gas phase deposition, subsequently to be separated at its edges from the substrate and lifted out.
It has now been found that in this procedure, the step of preparing the first layer of the protection strip via electron beam induced gas phase deposition determines the speed of the entire process, because the subsequent ion beam induced deposition is much faster. On the other hand, conventionally, it was not feasible to dispense with this first, slow step, because the direct application of the ion would lead, by erosion or amorphisation, to the destruction of the structures to be inspected.
The present invention has been conceived to overcome the drawbacks of the prior art.